Reinforcement of innerspring assemblies is provided in many forms to firm up soft and/or poor-quality assemblies which have too few springs or too small gauge wires or to enable providing the desirable quality of firmness and durability without an excessive number of springs which complicate construction and increase the cost. Such devices have in the past been built into the assembly as the latter is constructed according to the specification of the manufacturer irrespective of and without opportunity on the part of the purchaser to decide where and how much reinforcement is desirable. The present invention is to provide structures which may be optionally applied to an already constructed spring assembly at one or more places according to customer wishes or which may be built into the assembly during construction of the latter according to customer specification which will add substantially to the comfort and appearance by minimizing sinking intermediate the longitudinal edges, bowing at the longitudinal edges and collapse of the longitudinal edges without involving time-consuming techniques and/or special machinery.